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Olson DG, Maloney MI, Lanahan AA, Cervenka ND, Xia Y, Pech-Canul A, Hon S, Tian L, Ziegler SJ, Bomble YJ, Lynd LR. Ethanol tolerance in engineered strains of Clostridium thermocellum. Biotechnol Biofuels Bioprod 2023; 16:137. [PMID: 37710260 PMCID: PMC10503014 DOI: 10.1186/s13068-023-02379-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Accepted: 08/05/2023] [Indexed: 09/16/2023]
Abstract
Clostridium thermocellum is a natively cellulolytic bacterium that is promising candidate for cellulosic biofuel production, and can produce ethanol at high yields (75-80% of theoretical) but the ethanol titers produced thus far are too low for commercial application. In several strains of C. thermocellum engineered for increased ethanol yield, ethanol titer seems to be limited by ethanol tolerance. Previous work to improve ethanol tolerance has focused on the WT organism. In this work, we focused on understanding ethanol tolerance in several engineered strains of C. thermocellum. We observed a tradeoff between ethanol tolerance and production. Adaptation for increased ethanol tolerance decreases ethanol production. Second, we observed a consistent genetic response to ethanol stress involving mutations at the AdhE locus. These mutations typically reduced NADH-linked ADH activity. About half of the ethanol tolerance phenotype could be attributed to the elimination of NADH-linked activity based on a targeted deletion of adhE. Finally, we observed that rich growth medium increases ethanol tolerance, but this effect is eliminated in an adhE deletion strain. Together, these suggest that ethanol inhibits growth and metabolism via a redox-imbalance mechanism. The improved understanding of mechanisms of ethanol tolerance described here lays a foundation for developing strains of C. thermocellum with improved ethanol production.
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Affiliation(s)
- Daniel G Olson
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA.
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA.
| | - Marybeth I Maloney
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Anthony A Lanahan
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Nicholas D Cervenka
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Ying Xia
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA
- College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, China
| | - Angel Pech-Canul
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Shuen Hon
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Liang Tian
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
- Youth Olympic Village, #1-1-602, Jianye District, Nanjing, Jiangsu, China
| | - Samantha J Ziegler
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
- National Renewable Energy Laboratory, Golden, CO, 80401, USA
| | - Yannick J Bomble
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
- National Renewable Energy Laboratory, Golden, CO, 80401, USA
| | - Lee R Lynd
- Thayer School of Engineering at Dartmouth College, Hanover, NH, 03755, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
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Daley SR, Gallanosa PM, Sparling R. Kinetic characterization of annotated glycolytic enzymes present in cellulose-fermenting Clostridium thermocellum suggests different metabolic roles. Biotechnol Biofuels Bioprod 2023; 16:112. [PMID: 37438781 DOI: 10.1186/s13068-023-02362-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Accepted: 06/27/2023] [Indexed: 07/14/2023]
Abstract
BACKGROUND The efficient production of sustainable biofuels is important for the reduction of greenhouse gas emissions. Clostridium thermocellum ATCC 27405 is a candidate for ethanol production from lignocellulosic biomass using consolidated bioprocessing. Fermentation of cellulosic biomass goes through an atypical glycolytic pathway in this thermophilic bacterium, with various glycolytic enzymes capable of utilizing different phosphate donors, including GTP and inorganic pyrophosphate (PPi), in addition to or in place of the usual ATP. C. thermocellum contains three annotated phosphofructokinases (PFK) genes, the expression of which have all been detected through proteomics and transcriptomics. Pfp (Cthe_0347) was previously characterized as pyrophosphate dependent with fructose-6-phosphate (F6P) as its substrate. RESULTS We now demonstrate that this enzyme can also phosphorylate sedoheptulose-7-phosphate (an intermediate in the pentose phosphate pathway), with the Vmax and Km of F6P being approximately 15 folds higher and 43 folds lower, respectively, in comparison to sedoheptulose-7-phosphate. Purified PfkA shows preference for GTP as the phosphate donor as opposed to ATP with a 12.5-fold difference in Km values while phosphorylating F6P. Allosteric regulation is a factor at play in PfkA activity, with F6P exhibiting positive cooperativity, and an apparent requirement for ammonium ions to attain maximal activity. Phosphoenolpyruvate and PPi were the only inhibitors for PfkA determined from the study, which corroborates what is known about enzymes from this subfamily. The activation or inhibition by these ligands lends support to the argument that glycolysis is regulated by metabolites such as PPi and NH4+ in the organism. PfkB, showed no activity with F6P, but had significant activity with fructose, while utilizing either ATP or GTP, making it a fructokinase. Rounding out the upper glycolysis pathway, the identity of the fructose-1,6-bisphosphate aldolase in the genome was verified and reported to have substantial activity with fructose-1,6-bisphosphate, in the presence of the divalent ion, Zn2+. CONCLUSION These findings along with previous proteomic data suggest that Pfp, plays a role in both glycolysis and the pentose phosphate pathway, while PfkA and PfkB may phosphorylate sugars in glycolysis but is responsible for sugar metabolism elsewhere under conditions outside of growth on sufficient cellobiose.
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Affiliation(s)
- Steve R Daley
- Department of Microbiology, University of Manitoba, 213 Buller Building, Winnipeg, MB, R3T 2N2, Canada
| | - Patricia Mae Gallanosa
- Department of Microbiology, University of Manitoba, 213 Buller Building, Winnipeg, MB, R3T 2N2, Canada
| | - Richard Sparling
- Department of Microbiology, University of Manitoba, 213 Buller Building, Winnipeg, MB, R3T 2N2, Canada.
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Kuil T, Nurminen CMK, van Maris AJA. Pyrophosphate as allosteric regulator of ATP-phosphofructokinase in Clostridium thermocellum and other bacteria with ATP- and PP i-phosphofructokinases. Arch Biochem Biophys 2023; 743:109676. [PMID: 37380119 DOI: 10.1016/j.abb.2023.109676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 06/13/2023] [Accepted: 06/17/2023] [Indexed: 06/30/2023]
Abstract
The phosphofructokinase (Pfk) reaction represents one of the key regulatory points in glycolysis. While most organisms encode for Pfks that use ATP as phosphoryl donor, some organisms also encode for PPi-dependent Pfks. Despite this central role, the biochemical characteristics as well as the physiological role of both Pfks is often not known. Clostridium thermocellum is an example of a microorganism that encodes for both Pfks, however, only PPi-Pfk activity has been detected in cell-free extracts and little is known about the regulation and function of both enzymes. In this study, the ATP- and PPi-Pfk of C. thermocellum were purified and biochemically characterized. No allosteric regulators were found for PPi-Pfk amongst common effectors. With fructose-6-P, PPi, fructose-1,6-bisP, and Pi PPi-Pfk showed high specificity (KM < 0.62 mM) and maximum activity (Vmax > 156 U mg-1). In contrast, ATP-Pfk showed much lower affinity (K0.5 of 9.26 mM) and maximum activity (14.5 U mg-1) with fructose-6-P. In addition to ATP, also GTP, UTP and ITP could be used as phosphoryl donors. The catalytic efficiency with GTP was 7-fold higher than with ATP, suggesting that GTP is the preferred substrate. The enzyme was activated by NH4+, and pronounced inhibition was observed with GDP, FBP, PEP, and especially with PPi (Ki of 0.007 mM). Characterization of purified ATP-Pfks originating from eleven different bacteria, encoding for only ATP-Pfk or for both ATP- and PPi-Pfk, identified that PPi inhibition of ATP-Pfks could be a common phenomenon for organisms with a PPi-dependent glycolysis.
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Affiliation(s)
- Teun Kuil
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Carolus M K Nurminen
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Antonius J A van Maris
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden.
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Sharma BD, Olson DG, Giannone RJ, Hettich RL, Lynd LR. Characterization and Amelioration of Filtration Difficulties Encountered in Metabolomic Studies of Clostridium thermocellum at Elevated Sugar Concentrations. Appl Environ Microbiol 2023; 89:e0040623. [PMID: 37039651 PMCID: PMC10132107 DOI: 10.1128/aem.00406-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Accepted: 03/12/2023] [Indexed: 04/12/2023] Open
Abstract
Clostridium thermocellum, a promising candidate for consolidated bioprocessing, has been subjected to numerous engineering strategies for enhanced bioethanol production. Measurements of intracellular metabolites at substrate concentrations high enough (>50 g/L) to allow the production of industrially relevant titers of ethanol would inform efforts toward this end but have been difficult due to the production of a viscous substance that interferes with the filtration and quenching steps during metabolite extraction. To determine whether this problem is unique to C. thermocellum, we performed filtration experiments with other organisms that have been engineered for high-titer ethanol production, including Escherichia coli and Thermoanaerobacterium saccharolyticum. We addressed the problem through a series of improvements, including active pH control (to reduce problems with viscosity), investigation of different filter materials and pore sizes (to increase the filtration capacity), and correction for extracellular metabolite concentrations, and we developed a technique for more accurate intracellular metabolite measurements at elevated substrate concentrations. IMPORTANCE The accurate measurement of intracellular metabolites (metabolomics) is an integral part of metabolic engineering for the enhanced production of industrially important compounds and a useful technique to understand microbial physiology. Previous work tended to focus on model organisms under laboratory conditions. As we try to perform metabolomic studies with a wider range of organisms under conditions that more closely represent those found in nature or industry, we have found limitations in existing techniques. For example, fast filtration is an important step in quenching metabolism in preparation for metabolite extraction; however, it does not work for cultures of C. thermocellum at high substrate concentrations. In this work, we characterize the extent of the problem and develop techniques to overcome it.
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Affiliation(s)
- Bishal D. Sharma
- Thayer School of Engineering at Dartmouth College, Hanover, New Hampshire, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Daniel G. Olson
- Thayer School of Engineering at Dartmouth College, Hanover, New Hampshire, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Richard J. Giannone
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Robert L. Hettich
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Lee R. Lynd
- Thayer School of Engineering at Dartmouth College, Hanover, New Hampshire, USA
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
- Enchi Corporation, Holliston, Massachusetts, USA
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Schroeder WL, Kuil T, van Maris AJA, Olson DG, Lynd LR, Maranas CD. A detailed genome-scale metabolic model of Clostridium thermocellum investigates sources of pyrophosphate for driving glycolysis. Metab Eng 2023; 77:306-322. [PMID: 37085141 DOI: 10.1016/j.ymben.2023.04.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/24/2023] [Accepted: 04/08/2023] [Indexed: 04/23/2023]
Abstract
Lignocellulosic biomass is an abundant and renewable source of carbon for chemical manufacturing, yet it is cumbersome in conventional processes. A promising, and increasingly studied, candidate for lignocellulose bioprocessing is the thermophilic anaerobe Clostridium thermocellum given its potential to produce ethanol, organic acids, and hydrogen gas from lignocellulosic biomass under high substrate loading. Possessing an atypical glycolytic pathway which substitutes GTP or pyrophosphate (PPi) for ATP in some steps, including in the energy-investment phase, identification, and manipulation of PPi sources are key to engineering its metabolism. Previous efforts to identify the primary pyrophosphate have been unsuccessful. Here, we explore pyrophosphate metabolism through reconstructing, updating, and analyzing a new genome-scale stoichiometric model for C. thermocellum, iCTH669. Hundreds of changes to the former GEM, iCBI655, including correcting cofactor usages, addressing charge and elemental balance, standardizing biomass composition, and incorporating the latest experimental evidence led to a MEMOTE score improvement to 94%. We found agreement of iCTH669 model predictions across all available fermentation and biomass yield datasets. The feasibility of hundreds of PPi synthesis routes, newly identified and previously proposed, were assessed through the lens of the iCTH669 model including biomass synthesis, tRNA synthesis, newly identified sources, and previously proposed PPi-generating cycles. In all cases, the metabolic cost of PPi synthesis is at best equivalent to investment of one ATP suggesting no direct energetic advantage for the cofactor substitution in C. thermocellum. Even though no unique source of PPi could be gleaned by the model, by combining with gene expression data two most likely scenarios emerge. First, previously investigated PPi sources likely account for most PPi production in wild-type strains. Second, alternate metabolic routes as encoded by iCTH669 can collectively maintain PPi levels even when previously investigated synthesis cycles are disrupted. Model iCTH669 is available at github.com/maranasgroup/iCTH669.
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Affiliation(s)
- Wheaton L Schroeder
- Department of Chemical Engineering, The Pennsylvania State University, University Park, PA, USA; Center for Bioenergy Innovation, Oak Ridge, TN, USA
| | - Teun Kuil
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Antonius J A van Maris
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Daniel G Olson
- Center for Bioenergy Innovation, Oak Ridge, TN, USA; Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
| | - Lee R Lynd
- Center for Bioenergy Innovation, Oak Ridge, TN, USA; Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
| | - Costas D Maranas
- Department of Chemical Engineering, The Pennsylvania State University, University Park, PA, USA; Center for Bioenergy Innovation, Oak Ridge, TN, USA.
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Cho DH, Kim HJ, Oh SJ, Hwang JH, Shin N, Bhatia SK, Yoon JJ, Jeon JM, Yang YH. Strategy for efficiently utilizing Escherichia coli cells producing isobutanol by combining isobutanol and indigo production systems. J Biotechnol 2023; 367:62-70. [PMID: 37019156 DOI: 10.1016/j.jbiotec.2023.03.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 03/30/2023] [Accepted: 03/31/2023] [Indexed: 04/05/2023]
Abstract
Isobutanol is a potential biofuel, and its microbial production systems have demonstrated promising results. In a microbial system, the isobutanol produced is secreted into the media; however, the cells remaining after fermentation cannot be used efficiently during the isobutanol recovery process and are discarded as waste. To address this, we aimed to investigate the strategy of utilizing these remaining cells by combining the isobutanol production system with the indigo production system, wherein the product accumulates intracellularly. Accordingly, we constructed E. coli systems with genes, such as acetolactate synthase gene (alsS), ketol-acid reductoisomerase gene (ilvC), dihydroxyl-acid dehydratase (ilvD), and alpha-ketoisovalerate decarboxylase gene (kivD), for isobutanol production and genes, such as tryptophanase gene (tnaA) and flavin-containing monooxygenase gene (FMO), for indigo production. This system produced isobutanol and indigo simultaneously while accumulating indigo within cells. The production of isobutanol and indigo exhibited a strong linear correlation up to 72 h of production time; however, the pattern of isobutanol and indigo production varied. To our knowledge, this study is the first to simultaneously produce isobutanol and indigo and can potentially enhance the economy of biochemical production.
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Affiliation(s)
- Do Hyun Cho
- Department of Biological Engineering, College of Engineering, Konkuk University, 120, Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
| | - Hyun Jin Kim
- Department of Biological Engineering, College of Engineering, Konkuk University, 120, Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
| | - Suk Jin Oh
- Department of Biological Engineering, College of Engineering, Konkuk University, 120, Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
| | - Jeong Hyeon Hwang
- Department of Biological Engineering, College of Engineering, Konkuk University, 120, Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
| | - Nara Shin
- Department of Biological Engineering, College of Engineering, Konkuk University, 120, Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
| | - Shashi Kant Bhatia
- Department of Biological Engineering, College of Engineering, Konkuk University, 120, Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea; Institute for Ubiquitous Information Technology and Applications, Konkuk University, Seoul, South Korea
| | - Jeong-Jun Yoon
- Green & Sustainable Materials R&D Department, Korea Institute of Industrial Technology (KITECH), Cheonan, Republic of Korea
| | - Jong-Min Jeon
- Green & Sustainable Materials R&D Department, Korea Institute of Industrial Technology (KITECH), Cheonan, Republic of Korea.
| | - Yung-Hun Yang
- Department of Biological Engineering, College of Engineering, Konkuk University, 120, Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea; Institute for Ubiquitous Information Technology and Applications, Konkuk University, Seoul, South Korea.
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Yayo J, Rydzak T, Kuil T, Karlsson A, Harding DJ, Guss AM, van Maris AJA. The Roles of Nicotinamide Adenine Dinucleotide Phosphate Reoxidation and Ammonium Assimilation in the Secretion of Amino Acids as Byproducts of Clostridium thermocellum. Appl Environ Microbiol 2023; 89:e0175322. [PMID: 36625594 DOI: 10.1128/aem.01753-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Clostridium thermocellum is a cellulolytic thermophile that is considered for the consolidated bioprocessing of lignocellulose to ethanol. Improvements in ethanol yield are required for industrial implementation, but the incompletely understood causes of amino acid secretion impede progress. In this study, amino acid secretion was investigated via gene deletions in ammonium-regulated, nicotinamide adenine dinucleotide phosphate (NADPH)-supplying and NADPH-consuming pathways as well as via physiological characterization in cellobiose-limited or ammonium-limited chemostats. First, the contribution of the NADPH-supplying malate shunt was studied with strains using either the NADPH-yielding malate shunt (Δppdk) or a redox-independent conversion of PEP to pyruvate (Δppdk ΔmalE::Peno-pyk). In the latter, branched-chain amino acids, especially valine, were significantly reduced, whereas the ethanol yield increased from 46 to 60%, suggesting that the secretion of these amino acids balances the NADPH surplus from the malate shunt. The unchanged amino acid secretion in Δppdk falsified a previous hypothesis on an ammonium-regulated PEP-to-pyruvate flux redistribution. The possible involvement of another NADPH-supplier, namely, NADH-dependent reduced ferredoxin:NADP+ oxidoreductase (nfnAB), was also excluded. Finally, the deletion of glutamate synthase (gogat) in ammonium assimilation resulted in the upregulation of NADPH-linked glutamate dehydrogenase activity and decreased amino acid yields. Since gogat in C. thermocellum is putatively annotated as ferredoxin-linked, a claim which is supported by the product redistribution observed in this study, this deletion likely replaced ferredoxin with NADPH in ammonium assimilation. Overall, these findings indicate that a need to reoxidize NADPH is driving the observed amino acid secretion, likely at the expense of the NADH needed for ethanol formation. This suggests that metabolic engineering strategies that simplify the redox metabolism and ammonium assimilation can contribute to increased ethanol yields. IMPORTANCE Improving the ethanol yield of C. thermocellum is important for the industrial implementation of this microorganism in consolidated bioprocessing. A central role of NADPH in driving amino acid byproduct formation was demonstrated by eliminating the NADPH-supplying malate shunt and separately by changing the cofactor specificity in ammonium assimilation. With amino acid secretion diverting carbon and electrons away from ethanol, these insights are important for further metabolic engineering to reach industrial requirements on ethanol yield. This study also provides chemostat data that are relevant for training genome-scale metabolic models and for improving the validity of their predictions, especially considering the reduced degree-of-freedom in the redox metabolism of the strains generated here. In addition, this study advances the fundamental understanding on the mechanisms underlying amino acid secretion in cellulolytic Clostridia as well as on the regulation and cofactor specificity in ammonium assimilation. Together, these efforts aid in the development of C. thermocellum for the sustainable consolidated bioprocessing of lignocellulose to ethanol with minimal pretreatment.
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Bing RG, Carey MJ, Laemthong T, Willard DJ, Crosby JR, Sulis DB, Wang JP, Adams MWW, Kelly RM. Fermentative conversion of unpretreated plant biomass: A thermophilic threshold for indigenous microbial growth. Bioresour Technol 2023; 367:128275. [PMID: 36347479 PMCID: PMC10561188 DOI: 10.1016/j.biortech.2022.128275] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 10/31/2022] [Accepted: 11/01/2022] [Indexed: 06/16/2023]
Abstract
Naturally occurring, microbial contaminants were found in plant biomasses from common bioenergy crops and agricultural wastes. Unexpectedly, indigenous thermophilic microbes were abundant, raising the question of whether they impact thermophilic consolidated bioprocessing fermentations that convert biomass directly into useful bioproducts. Candidate microbial platforms for biomass conversion, Acetivibrio thermocellus (basionym Clostridium thermocellum; Topt 60 °C) and Caldicellulosiruptor bescii (Topt 78 °C), each degraded a wide variety of plant biomasses, but only A. thermocellus was significantly affected by the presence of indigenous microbial populations harbored by the biomass. Indigenous microbial growth was eliminated at ≥75 °C, conditions where C. bescii thrives, but where A. thermocellus cannot survive. Therefore, 75 °C is the thermophilic threshold to avoid sterilizing pre-treatments on the biomass that prevents native microbes from competing with engineered microbes and forming undesirable by-products. Thermophiles that naturally grow at and above 75 °C offer specific advantages as platform microorganisms for biomass conversion into fuels and chemicals.
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Affiliation(s)
- Ryan G Bing
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, United States
| | - Morgan J Carey
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, United States
| | - Tunyaboon Laemthong
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, United States
| | - Daniel J Willard
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, United States
| | - James R Crosby
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, United States
| | - Daniel B Sulis
- Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695, United States
| | - Jack P Wang
- Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695, United States
| | - Michael W W Adams
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, United States
| | - Robert M Kelly
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, United States.
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Kuil T, Yayo J, Pechan J, Küchler J, van Maris AJA. Ethanol tolerance of Clostridium thermocellum: the role of chaotropicity, temperature and pathway thermodynamics on growth and fermentative capacity. Microb Cell Fact 2022; 21:273. [PMID: 36567317 PMCID: PMC9790125 DOI: 10.1186/s12934-022-01999-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Accepted: 12/17/2022] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Clostridium thermocellum is a promising candidate for consolidated bioprocessing of lignocellulosic biomass to ethanol. The low ethanol tolerance of this microorganism is one of the remaining obstacles to industrial implementation. Ethanol inhibition can be caused by end-product inhibition and/or chaotropic-induced stress resulting in increased membrane fluidization and disruption of macromolecules. The highly reversible glycolysis of C. thermocellum might be especially sensitive to end-product inhibition. The chaotropic effect of ethanol is known to increase with temperature. This study explores the relative contributions of these two aspects to investigate and possibly mitigate ethanol-induced stress in growing and non-growing C. thermocellum cultures. RESULTS To separate chaotropic from thermodynamic effects of ethanol toxicity, a non-ethanol producing strain AVM062 (Pclo1313_2638::ldh* ∆adhE) was constructed by deleting the bifunctional acetaldehyde/alcohol dehydrogenase gene, adhE, in a lactate-overproducing strain. Exogenously added ethanol lowered the growth rate of both wild-type and the non-ethanol producing mutant. The mutant strain grew quicker than the wild-type at 50 and 55 °C for ethanol concentrations ≥ 10 g L-1 and was able to reach higher maximum OD600 at all ethanol concentrations and temperatures. For the wild-type, the maximum OD600 and relative growth rates were higher at 45 and 50 °C, compared to 55 °C, for ethanol concentrations ≥ 15 g L-1. For the mutant strain, no positive effect on growth was observed at lower temperatures. Growth-arrested cells of the wild-type demonstrated improved fermentative capacity over time in the presence of ethanol concentrations up to 40 g L-1 at 45 and 50 °C compared to 55 °C. CONCLUSION Positive effects of temperature on ethanol tolerance were limited to wild-type C. thermocellum and are likely related to mechanisms involved in the ethanol-formation pathway and redox cofactor balancing. Lowering the cultivation temperature provides an attractive strategy to improve growth and fermentative capacity at high ethanol titres in high-cellulose loading batch cultivations. Finally, non-ethanol producing strains are useful platform strains to study the effects of chaotropicity and thermodynamics related to ethanol toxicity and allow for deeper understanding of growth and/or fermentation cessation under industrially relevant conditions.
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Affiliation(s)
- Teun Kuil
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Johannes Yayo
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Johanna Pechan
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Jan Küchler
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden ,grid.5807.a0000 0001 1018 4307Present Address: Max Plank Institute for Dynamics of Complex Technical Systems, Otto-Von-Guericke-University Magdeburg, Magdeburg, Germany
| | - Antonius J. A. van Maris
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
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10
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Hon S, Jacobson T, Stevenson DM, Maloney MI, Giannone RJ, Hettich RL, Amador-noguez D, Olson DG, Lynd LR. Increasing the Thermodynamic Driving Force of the Phosphofructokinase Reaction in Clostridium thermocellum. Appl Environ Microbiol 2022. [PMID: 36286488 PMCID: PMC9680637 DOI: 10.1128/aem.01258-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ability to control the distribution of thermodynamic driving force throughout a metabolic pathway is likely to be an important tool for metabolic engineering. The phosphofructokinase reaction is a key enzyme in Embden-Mayerhof-Parnas glycolysis and therefore improving the thermodynamic driving force of this reaction in
C. thermocellum
is believed to enable higher product titers.
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11
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Sha C, Wang Q, Wang H, Duan Y, Xu C, Wu L, Ma K, Shao W, Jiang Y. Characterization of Thermotoga neapolitana Alcohol Dehydrogenases in the Ethanol Fermentation Pathway. Biology 2022; 11:biology11091318. [PMID: 36138797 PMCID: PMC9495900 DOI: 10.3390/biology11091318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 08/26/2022] [Accepted: 09/01/2022] [Indexed: 11/16/2022]
Abstract
Hyperthermophilic Thermotoga spp. are candidates for cellulosic ethanol fermentation. A bifunctional iron-acetaldehyde/alcohol dehydrogenase (Fe-AAdh) has been revealed to catalyze the acetyl-CoA (Ac-CoA) reduction to form ethanol via an acetaldehyde intermediate in Thermotoga neapolitana (T. neapolitana). In this organism, there are three additional alcohol dehydrogenases, Zn-Adh, Fe-Adh1, and Fe-Adh2, encoded by genes CTN_0257, CTN_1655, and CTN_1756, respectively. This paper reports the properties and functions of these enzymes in the fermentation pathway from Ac-CoA to ethanol. It was determined that Zn-Adh only exhibited activity when oxidizing ethanol to acetaldehyde, and no detectable activity for the reaction from acetaldehyde to ethanol. Fe-Adh1 had specific activities of approximately 0.7 and 0.4 U/mg for the forward and reverse reactions between acetaldehyde and ethanol at a pHopt of 8.5 and Topt of 95 °C. Catalyzing the reduction of acetaldehyde to produce ethanol, Fe-Adh2 exhibited the highest activity of approximately 3 U/mg at a pHopt of 7.0 and Topt of 85 °C, which were close to the optimal growth conditions. These results indicate that Fe-Adh2 and Zn-Adh are the main enzymes that catalyze ethanol formation and consumption in the hyperthermophilic bacterium, respectively.
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Affiliation(s)
- Chong Sha
- Biofuels Institute, School of the Environment, Jiangsu University, Zhenjiang 212013, China
| | - Qiang Wang
- Biofuels Institute, School of the Environment, Jiangsu University, Zhenjiang 212013, China
- School of Biological and Food Engineering, Suzhou University, Bianhe Middle Road 49, Suzhou 234000, China
| | - Hongcheng Wang
- Biofuels Institute, School of the Environment, Jiangsu University, Zhenjiang 212013, China
| | - Yilan Duan
- School of Biological and Food Engineering, Suzhou University, Bianhe Middle Road 49, Suzhou 234000, China
| | - Chongmao Xu
- Huzhou Research Center of Industrial Biotechnology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Huzhou 313000, China
| | - Lian Wu
- Huzhou Research Center of Industrial Biotechnology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Huzhou 313000, China
| | - Kesen Ma
- Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Weilan Shao
- Shine E BioTech (Nanjing) Company, Nanjing 210023, China
- Correspondence: (W.S.); (Y.J.)
| | - Yu Jiang
- Huzhou Research Center of Industrial Biotechnology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Huzhou 313000, China
- Correspondence: (W.S.); (Y.J.)
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12
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Chirania P, Holwerda EK, Giannone RJ, Liang X, Poudel S, Ellis JC, Bomble YJ, Hettich RL, Lynd LR. Metaproteomics reveals enzymatic strategies deployed by anaerobic microbiomes to maintain lignocellulose deconstruction at high solids. Nat Commun 2022; 13. [PMID: 35790765 PMCID: PMC9256739 DOI: 10.1038/s41467-022-31433-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Accepted: 06/16/2022] [Indexed: 11/08/2022] Open
Abstract
AbstractEconomically viable production of cellulosic biofuels requires operation at high solids loadings—on the order of 15 wt%. To this end we characterize Nature’s ability to deconstruct and utilize mid-season switchgrass at increasing solid loadings using an anaerobic methanogenic microbiome. This community exhibits undiminished fractional carbohydrate solubilization at loadings ranging from 30 g/L to 150 g/L. Metaproteomic interrogation reveals marked increases in the abundance of specific carbohydrate-active enzyme classes. Significant enrichment of auxiliary activity family 6 enzymes at higher solids suggests a role for Fenton chemistry. Stress-response proteins accompanying these reactions are similarly upregulated at higher solids, as are β-glucosidases, xylosidases, carbohydrate-debranching, and pectin-acting enzymes—all of which indicate that removal of deconstruction inhibitors is important for observed undiminished solubilization. Our work provides insights into the mechanisms by which natural microbiomes effectively deconstruct and utilize lignocellulose at high solids loadings, informing the future development of defined cultures for efficient bioconversion.
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13
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Kubis MR, Holwerda EK, Lynd LR. Declining carbohydrate solubilization with increasing solids loading during fermentation of cellulosic feedstocks by Clostridium thermocellum: documentation and diagnostic tests. Biotechnol Biofuels Bioprod 2022; 15:12. [PMID: 35418299 PMCID: PMC8817502 DOI: 10.1186/s13068-022-02110-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Accepted: 01/15/2022] [Indexed: 12/31/2022]
Abstract
Background For economically viable 2nd generation biofuels, processing of high solid lignocellulosic substrate concentrations is a necessity. The cellulolytic thermophilic anaerobe Clostridium thermocellum is one of the most effective biocatalysts for solubilization of carbohydrate harbored in lignocellulose. This study aims to document the solubilization performance of Clostridium thermocellum at increasing solids concentrations for two lignocellulosic feedstocks, corn stover and switchgrass, and explore potential effectors of solubilization performance. Results Monocultures of Clostridium thermocellum demonstrated high levels of carbohydrate solubilization for both unpretreated corn stover and switchgrass. However, fractional carbohydrate solubilization decreases with increasing solid loadings. Fermentation of model insoluble substrate (cellulose) in the presence of high solids lignocellulosic spent broth is temporarily affected but not model soluble substrate (cellobiose) fermentations. Mid-fermentation addition of cells (C. thermocellum) or model substrates did not significantly enhance overall corn stover solubilization loaded at 80 g/L, however cultures utilized the model substrates in the presence of high concentrations of corn stover. An increase in corn stover solubilization was observed when water was added, effectively diluting the solids concentration mid-fermentation. Introduction of a hemicellulose-utilizing coculture partner, Thermoanaerobacterium thermosaccharolyticum, increased the fractional carbohydrate solubilization at both high and low solid loadings. Residual solubilized carbohydrates diminished significantly in the presence of T. thermosaccharolyticum compared to monocultures of C. thermocellum, yet a small fraction of solubilized oligosaccharides of both C5 and C6 sugars remained unutilized. Conclusion Diminishing fractional carbohydrate solubilization with increasing substrate loading was observed for C. thermocellum-mediated solubilization and fermentation of unpretreated lignocellulose feedstocks. Results of experiments involving spent broth addition do not support a major role for inhibitors present in the liquid phase. Mid-fermentation addition experiments confirm that C. thermocellum and its enzymes remain capable of converting model substrates during the middle of high solids lignocellulose fermentation. An increase in fractional carbohydrate solubilization was made possible by (1) mid-fermentation solid loading dilutions and (2) coculturing C. thermocellum with T. thermosaccharolyticum, which ferments solubilized hemicellulose. Incomplete utilization of solubilized carbohydrates suggests that a small fraction of the carbohydrates is unaffected by the extracellular carbohydrate-active enzymes present in the culture. Supplementary Information The online version contains supplementary material available at 10.1186/s13068-022-02110-4.
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Affiliation(s)
- Matthew R Kubis
- Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA.,The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Evert K Holwerda
- Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA. .,The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
| | - Lee R Lynd
- Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA.,The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
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Lanahan A, Zakowicz K, Tian L, Olson DG, Lynd LR. A Single Nucleotide Change in the polC DNA Polymerase III in Clostridium thermocellum Is Sufficient To Create a Hypermutator Phenotype. Appl Environ Microbiol 2022; 88:e0153121. [PMID: 35015978 DOI: 10.1128/AEM.01531-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Clostridium thermocellum is a thermophilic, anaerobic bacterium that natively ferments cellulose to ethanol and is a candidate for cellulosic biofuel production. Recently, we identified a hypermutator strain of C. thermocellum with a C669Y mutation in the polC gene, which encodes a DNA polymerase III enzyme. Here, we reintroduced this mutation using recently developed CRISPR tools to demonstrate that this mutation is sufficient to recreate the hypermutator phenotype. The resulting strain shows an approximately 30-fold increase in the mutation rate. This mutation is hypothesized to function by interfering with metal ion coordination in the PHP (polymerase and histidinol phosphatase) domain, which is responsible for proofreading. The ability to selectively increase the mutation rate in C. thermocellum is a useful tool for future directed evolution experiments. IMPORTANCE Cellulosic biofuels are a promising approach to decarbonize the heavy-duty-transportation sector. A longstanding barrier to cost-effective cellulosic biofuel production is the recalcitrance of cellulose to solubilization. Native cellulose-consuming organisms, such as Clostridium thermocellum, are promising candidates for cellulosic biofuel production; however, they often need to be genetically modified to improve product formation. One approach is adaptive laboratory evolution. Our findings demonstrate a way to increase the mutation rate in this industrially relevant organism, which can reduce the time needed for adaptive evolution experiments.
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15
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Kuil T, Hon S, Yayo J, Foster C, Ravagnan G, Maranas CD, Lynd LR, Olson DG, van Maris AJA. Functional analysis of H +-pumping membrane-bound pyrophosphatase, ADP-glucose synthase, and pyruvate phosphate dikinase as pyrophosphate sources in Clostridium thermocellum. Appl Environ Microbiol 2021;:AEM0185721. [PMID: 34936842 DOI: 10.1128/AEM.01857-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The atypical glycolysis of Clostridium thermocellum is characterized by the use of pyrophosphate (PPi) as phosphoryl donor for phosphofructokinase (Pfk) and pyruvate phosphate dikinase (Ppdk) reactions. Previously, biosynthetic PPi was calculated to be stoichiometrically insufficient to drive glycolysis. This study investigates the role of a H+-pumping membrane-bound pyrophosphatase, glycogen cycling, a predicted Ppdk-malate shunt cycle and acetate cycling in generating PPi. Knockout studies and enzyme assays confirmed that clo1313_0823 encodes a membrane-bound pyrophosphatase. Additionally, clo1313_0717-0718 was confirmed to encode ADP-glucose synthase by knockouts, glycogen measurements in C. thermocellum and heterologous expression in E. coli. Unexpectedly, individually-targeted gene deletions of the four putative PPi sources did not have a significant phenotypic effect. Although combinatorial deletion of all four putative PPi sources reduced the growth rate by 22% (0.30±0.01 h-1) and the biomass yield by 38% (0.18±0.00 gbiomass gsubstrate-1), this change was much smaller than what would be expected for stoichiometrically essential PPi-supplying mechanisms. Growth-arrested cells of the quadruple knockout readily fermented cellobiose indicating that the unknown PPi-supplying mechanisms are independent of biosynthesis. An alternative hypothesis that ATP-dependent Pfk activity circumvents a need for PPi altogether, was falsified by enzyme assays, heterologous expression of candidate genes and whole-genome sequencing. As a secondary outcome, enzymatic assays confirmed functional annotation of clo1313_1832 as ATP- and GTP-dependent fructokinase. These results indicate that the four investigated PPi sources individually and combined play no significant PPi-supplying role and the true source(s) of PPi, or alternative phosphorylating mechanisms, that drive glycolysis in C. thermocellum remain(s) elusive. IMPORTANCE Increased understanding of the central metabolism of C. thermocellum is important from a fundamental as well as from a sustainability and industrial perspective. In addition to showing that H+-pumping membrane-bound PPase, glycogen cycling, a Ppdk-malate shunt cycle, and acetate cycling are not significant sources of PPi supply, this study adds functional annotation of four genes and availability of an updated PPi stoichiometry from biosynthesis to the scientific domain. Together, this aids future metabolic engineering attempts aimed to improve C. thermocellum as a cell factory for sustainable and efficient production of ethanol from lignocellulosic material through consolidated bioprocessing with minimal pretreatment. Getting closer to elucidating the elusive source of PPi, or alternative phosphorylating mechanisms, for the atypical glycolysis is itself of fundamental importance. Additionally, the findings of this study directly contribute to investigations into trade-offs between thermodynamic driving force versus energy yield of PPi- and ATP-dependent glycolysis.
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16
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Joseph RC, Kelley SQ, Kim NM, Sandoval NR. Metabolic Engineering and the Synthetic Biology Toolbox for
Clostridium. Metab Eng 2021. [DOI: 10.1002/9783527823468.ch16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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17
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Ha-Tran DM, Nguyen TTM, Lo SC, Huang CC. Utilization of Monosaccharides by Hungateiclostridium thermocellum ATCC 27405 through Adaptive Evolution. Microorganisms 2021; 9:1445. [PMID: 34361881 DOI: 10.3390/microorganisms9071445] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 06/30/2021] [Accepted: 07/02/2021] [Indexed: 12/13/2022] Open
Abstract
Hungateiclostridium thermocellum ATCC 27405 is a promising bacterium for consolidated bioprocessing with a robust ability to degrade lignocellulosic biomass through a multienzyme cellulosomal complex. The bacterium uses the released cellodextrins, glucose polymers of different lengths, as its primary carbon source and energy. In contrast, the bacterium exhibits poor growth on monosaccharides such as fructose and glucose. This phenomenon raises many important questions concerning its glycolytic pathways and sugar transport systems. Until now, the detailed mechanisms of H. thermocellum adaptation to growth on hexose sugars have been relatively poorly explored. In this study, adaptive laboratory evolution was applied to train the bacterium in hexose sugars-based media, and genome resequencing was used to detect the genes that got mutated during adaptation period. RNA-seq data of the first culture growing on either fructose or glucose revealed that several glycolytic genes in the Embden–Mayerhof–Parnas pathway were expressed at lower levels in these cells than in cellobiose-grown cells. After seven consecutive transfer events on fructose and glucose (~42 generations for fructose-adapted cells and ~40 generations for glucose-adapted cells), several genes in the EMP glycolysis of the evolved strains increased the levels of mRNA expression, accompanied by a faster growth, a greater biomass yield, a higher ethanol titer than those in their parent strains. Genomic screening also revealed several mutation events in the genomes of the evolved strains, especially in those responsible for sugar transport and central carbon metabolism. Consequently, these genes could be applied as potential targets for further metabolic engineering to improve this bacterium for bio-industrial usage.
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Bing RG, Sulis DB, Wang JP, Adams MW, Kelly RM. Thermophilic microbial deconstruction and conversion of natural and transgenic lignocellulose. Environ Microbiol Rep 2021; 13:272-293. [PMID: 33684253 PMCID: PMC10519370 DOI: 10.1111/1758-2229.12943] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 02/25/2021] [Accepted: 02/28/2021] [Indexed: 06/12/2023]
Abstract
The potential to convert renewable plant biomasses into fuels and chemicals by microbial processes presents an attractive, less environmentally intense alternative to conventional routes based on fossil fuels. This would best be done with microbes that natively deconstruct lignocellulose and concomitantly form industrially relevant products, but these two physiological and metabolic features are rarely and simultaneously observed in nature. Genetic modification of both plant feedstocks and microbes can be used to increase lignocellulose deconstruction capability and generate industrially relevant products. Separate efforts on plants and microbes are ongoing, but these studies lack a focus on optimal, complementary combinations of these disparate biological systems to obtain a convergent technology. Improving genetic tools for plants have given rise to the generation of low-lignin lines that are more readily solubilized by microorganisms. Most focus on the microbiological front has involved thermophilic bacteria from the genera Caldicellulosiruptor and Clostridium, given their capacity to degrade lignocellulose and to form bio-products through metabolic engineering strategies enabled by ever-improving molecular genetics tools. Bioengineering plant properties to better fit the deconstruction capabilities of candidate consolidated bioprocessing microorganisms has potential to achieve the efficient lignocellulose deconstruction needed for industrial relevance.
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Affiliation(s)
- Ryan G. Bing
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695
| | - Daniel B. Sulis
- Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695
| | - Jack P. Wang
- Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695
| | - Michael W.W. Adams
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602
| | - Robert M. Kelly
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695
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19
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Yayo J, Kuil T, Olson DG, Lynd LR, Holwerda EK, van Maris AJA. Laboratory Evolution and Reverse Engineering of Clostridium thermocellum for Growth on Glucose and Fructose. Appl Environ Microbiol 2021; 87:e03017-20. [PMID: 33608285 PMCID: PMC8091016 DOI: 10.1128/aem.03017-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2020] [Accepted: 02/10/2021] [Indexed: 02/04/2023] Open
Abstract
The native ability of Clostridium thermocellum to efficiently solubilize cellulose makes it an interesting platform for sustainable biofuel production through consolidated bioprocessing. Together with other improvements, industrial implementation of C. thermocellum, as well as fundamental studies into its metabolism, would benefit from improved and reproducible consumption of hexose sugars. To investigate growth of C. thermocellum on glucose or fructose, as well as the underlying molecular mechanisms, laboratory evolution was performed in carbon-limited chemostats with increasing concentrations of glucose or fructose and decreasing cellobiose concentrations. Growth on both glucose and fructose was achieved with biomass yields of 0.09 ± 0.00 and 0.18 ± 0.00 gbiomass gsubstrate-1, respectively, compared to 0.15 ± 0.01 gbiomass gsubstrate-1 for wild type on cellobiose. Single-colony isolates had no or short lag times on the monosaccharides, while wild type showed 42 ± 4 h on glucose and >80 h on fructose. With good growth on glucose, fructose, and cellobiose, the fructose isolates were chosen for genome sequence-based reverse metabolic engineering. Deletion of a putative transcriptional regulator (Clo1313_1831), which upregulated fructokinase activity, reduced lag time on fructose to 12 h with a growth rate of 0.11 ± 0.01 h-1 and resulted in immediate growth on glucose at 0.24 ± 0.01 h-1 Additional introduction of a G-to-V mutation at position 148 in cbpA resulted in immediate growth on fructose at 0.32 ± 0.03 h-1 These insights can guide engineering of strains for fundamental studies into transport and the upper glycolysis, as well as maximizing product yields in industrial settings.IMPORTANCEC. thermocellum is an important candidate for sustainable and cost-effective production of bioethanol through consolidated bioprocessing. In addition to unsurpassed cellulose deconstruction, industrial application and fundamental studies would benefit from improvement of glucose and fructose consumption. This study demonstrated that C. thermocellum can be evolved for reproducible constitutive growth on glucose or fructose. Subsequent genome sequencing, gene editing, and physiological characterization identified two underlying mutations with a role in (regulation of) transport or metabolism of the hexose sugars. In light of these findings, such mutations have likely (and unknowingly) also occurred in previous studies with C. thermocellum using hexose-based media with possible broad regulatory consequences. By targeted modification of these genes, industrial and research strains of C. thermocellum can be engineered to (i) reduce glucose accumulation, (ii) study cellodextrin transport systems in vivo, (iii) allow experiments at >120 g liter-1 soluble substrate concentration, or (iv) reduce costs for labeling studies.
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Affiliation(s)
- Johannes Yayo
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Teun Kuil
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Daniel G Olson
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
- The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Lee R Lynd
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
- The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Evert K Holwerda
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
- The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Antonius J A van Maris
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
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20
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Beri D, Herring CD, Blahova S, Poudel S, Giannone RJ, Hettich RL, Lynd LR. Coculture with hemicellulose-fermenting microbes reverses inhibition of corn fiber solubilization by Clostridium thermocellum at elevated solids loadings. Biotechnol Biofuels 2021; 14:24. [PMID: 33461608 PMCID: PMC7814735 DOI: 10.1186/s13068-020-01867-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Accepted: 12/24/2020] [Indexed: 05/10/2023]
Abstract
BACKGROUND The cellulolytic thermophile Clostridium thermocellum is an important biocatalyst due to its ability to solubilize lignocellulosic feedstocks without the need for pretreatment or exogenous enzyme addition. At low concentrations of substrate, C. thermocellum can solubilize corn fiber > 95% in 5 days, but solubilization declines markedly at substrate concentrations higher than 20 g/L. This differs for model cellulose like Avicel, on which the maximum solubilization rate increases in proportion to substrate concentration. The goal of this study was to examine fermentation at increasing corn fiber concentrations and investigate possible reasons for declining performance. RESULTS The rate of growth of C. thermocellum on corn fiber, inferred from CipA scaffoldin levels measured by LC-MS/MS, showed very little increase with increasing solids loading. To test for inhibition, we evaluated the effects of spent broth on growth and cellulase activity. The liquids remaining after corn fiber fermentation were found to be strongly inhibitory to growth on cellobiose, a substrate that does not require cellulose hydrolysis. Additionally, the hydrolytic activity of C. thermocellum cellulase was also reduced to less-than half by adding spent broth. Noting that > 15 g/L hemicellulose oligosaccharides accumulated in the spent broth of a 40 g/L corn fiber fermentation, we tested the effect of various model carbohydrates on growth on cellobiose and Avicel. Some compounds like xylooligosaccharides caused a decline in cellulolytic activity and a reduction in the maximum solubilization rate on Avicel. However, there were no relevant model compounds that could replicate the strong inhibition by spent broth on C. thermocellum growth on cellobiose. Cocultures of C. thermocellum with hemicellulose-consuming partners-Herbinix spp. strain LL1355 and Thermoanaerobacterium thermosaccharolyticum-exhibited lower levels of unfermented hemicellulose hydrolysis products, a doubling of the maximum solubilization rate, and final solubilization increased from 67 to 93%. CONCLUSIONS This study documents inhibition of C. thermocellum with increasing corn fiber concentration and demonstrates inhibition of cellulase activity by xylooligosaccharides, but further work is needed to understand why growth on cellobiose was inhibited by corn fiber fermentation broth. Our results support the importance of hemicellulose-utilizing coculture partners to augment C. thermocellum in the fermentation of lignocellulosic feedstocks at high solids loading.
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Affiliation(s)
- Dhananjay Beri
- Thayer School of Engineering, Dartmouth College, Hanover, NH, 03755, USA
- Centre for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Christopher D Herring
- Thayer School of Engineering, Dartmouth College, Hanover, NH, 03755, USA.
- Centre for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA.
- Enchi Corporation, Lebanon, NH, 03766, USA.
| | - Sofie Blahova
- Thayer School of Engineering, Dartmouth College, Hanover, NH, 03755, USA
| | - Suresh Poudel
- Centre for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Richard J Giannone
- Centre for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Robert L Hettich
- Centre for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Lee R Lynd
- Thayer School of Engineering, Dartmouth College, Hanover, NH, 03755, USA
- Centre for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
- Enchi Corporation, Lebanon, NH, 03766, USA
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Abstract
Environmental issues have prompted the vigorous development of biorefineries that use agricultural waste and other biomass feedstock as raw materials. However, most current biorefinery products are cellulosic ethanol. There is an urgent need for biorefineries to expand into new bioproducts. Isobutanol is an important bulk chemical with properties that are close to gasoline, making it a very promising biofuel. The use of microorganisms to produce isobutanol has been extensively studied, but there is still a considerable gap to achieving the industrial production of isobutanol from biomass. This review summarizes current metabolic engineering strategies that have been applied to biomass isobutanol production and recent advances in the production of isobutanol from different biomass feedstocks.
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Holwerda EK, Zhou J, Hon S, Stevenson DM, Amador-Noguez D, Lynd LR, van Dijken JP. Metabolic Fluxes of Nitrogen and Pyrophosphate in Chemostat Cultures of Clostridium thermocellum and Thermoanaerobacterium saccharolyticum. Appl Environ Microbiol 2020; 86:e01795-20. [PMID: 32978139 DOI: 10.1128/AEM.01795-20] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Accepted: 09/17/2020] [Indexed: 01/29/2023] Open
Abstract
Clostridium thermocellum and Thermoanaerobacterium saccharolyticum were grown in cellobiose-limited chemostat cultures at a fixed dilution rate. C. thermocellum produced acetate, ethanol, formate, and lactate. Surprisingly, and in contrast to batch cultures, in cellobiose-limited chemostat cultures of T. saccharolyticum, ethanol was the main fermentation product. Enzyme assays confirmed that in C. thermocellum, glycolysis proceeds via pyrophosphate (PPi)-dependent phosphofructokinase (PFK), pyruvate-phosphate dikinase (PPDK), as well as a malate shunt for the conversion of phosphoenolpyruvate (PEP) to pyruvate. Pyruvate kinase activity was not detectable. In T. saccharolyticum, ATP but not PPi served as cofactor for the PFK reaction. High activities of both pyruvate kinase and PPDK were present, whereas the activities of a malate shunt enzymes were low in T. saccharolyticum In C. thermocellum, glycolysis via PPi-PFK and PPDK obeys the equation glucose + 5 NDP + 3 PPi → 2 pyruvate + 5 NTP + Pi (where NDP is nucleoside diphosphate and NTP is nucleoside triphosphate). Metabolic flux analysis of chemostat data with the wild type and a deletion mutant of the proton-pumping pyrophosphatase showed that a PPi-generating mechanism must be present that operates according to ATP + Pi → ADP + PPi Both organisms also produced significant amounts of amino acids in cellobiose-limited cultures. It was anticipated that this phenomenon would be suppressed by growth under nitrogen limitation. Surprisingly, nitrogen-limited chemostat cultivation of wild-type C. thermocellum revealed a bottleneck in pyruvate oxidation, as large amounts of pyruvate and amino acids, mainly valine, were excreted; up to 50% of the nitrogen consumed was excreted again as amino acids.IMPORTANCE This study discusses the fate of pyrophosphate in the metabolism of two thermophilic anaerobes that lack a soluble irreversible pyrophosphatase as present in Escherichia coli but instead use a reversible membrane-bound proton-pumping enzyme. In such organisms, the charging of tRNA with amino acids may become more reversible. This may contribute to the observed excretion of amino acids during sugar fermentation by Clostridium thermocellum and Thermoanaerobacterium saccharolyticum Calculation of the energetic advantage of reversible pyrophosphate-dependent glycolysis, as occurs in Clostridium thermocellum, could not be properly evaluated, as currently available genome-scale models neglect the anabolic generation of pyrophosphate in, for example, polymerization of amino acids to protein. This anabolic pyrophosphate replaces ATP and thus saves energy. Its amount is, however, too small to cover the pyrophosphate requirement of sugar catabolism in glycolysis. Consequently, pyrophosphate for catabolism is generated according to ATP + Pi → ADP + PPi.
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Godara A, Kao KC. Adaptive laboratory evolution for growth coupled microbial production. World J Microbiol Biotechnol 2020; 36:175. [DOI: 10.1007/s11274-020-02946-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Accepted: 10/08/2020] [Indexed: 12/18/2022]
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Li Q, Zhao P, Yin H, Liu Z, Zhao H, Tian P. CRISPR interference-guided modulation of glucose pathways to boost aconitic acid production in Escherichia coli. Microb Cell Fact 2020; 19:174. [PMID: 32883305 PMCID: PMC7470443 DOI: 10.1186/s12934-020-01435-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 08/27/2020] [Indexed: 12/26/2022] Open
Abstract
Background One major mission of microbial breeding is high-level production of desired metabolites. Overproduction of intermediate metabolites in core pathways is challenging as it may impair cell growth and viability. Results Here we report that aconitic acid, an intermediate metabolite in tricarboxylic acid (TCA) cycle, can be overproduced by an engineered CRISPR interference (CRISPRi) system in Escherichia coli. This CRISPRi system was designed to simultaneously target pyruvate kinase (PK) and isocitrate dehydrogenase (IDH), two enzymes in glycolytic pathway and TCA cycle, respectively. Reverse transcription and quantitative PCR and enzyme activity assays showed that this engineered CRISPRi system significantly repressed the genes encoding IDH and PK, resulting in simultaneous reduction in the activities of IDH and PK. In shake-flask and fed-batch cultivation, this CRISPRi strain produced 60-fold (362.80 ± 22.05 mg/L) and 15-fold (623.80 ± 20.05 mg/L) of aconitic acid relative to the control strain, respectively. In addition, this two-target CRISPRi strain maintained low levels of acetate and lactate, two problematic byproducts. Conclusions This work demonstrates that CRISPRi system can improve aconitic acid production by coordinating glycolysis and TCA cycle. This study provides insights for high-level production of the intermediate metabolites in central pathways.
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Affiliation(s)
- Qingyang Li
- School of Food Science and Engineering, South China University of Technology, Guangzhou, 510641, China
| | - Peng Zhao
- College of Life Science and Technology, Beijing University of Chemical Technology, Beijing, 100029, China
| | - Hang Yin
- School of Food Science and Engineering, South China University of Technology, Guangzhou, 510641, China
| | - Zhaonan Liu
- College of Life Science and Technology, Beijing University of Chemical Technology, Beijing, 100029, China
| | - Haifeng Zhao
- School of Food Science and Engineering, South China University of Technology, Guangzhou, 510641, China
| | - Pingfang Tian
- College of Life Science and Technology, Beijing University of Chemical Technology, Beijing, 100029, China.
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Mazzoli R, Olson D. Clostridium thermocellum: A microbial platform for high-value chemical production from lignocellulose. Adv Appl Microbiol 2020; 113:111-161. [PMID: 32948265 DOI: 10.1016/bs.aambs.2020.07.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Second generation biorefining, namely fermentation processes based on lignocellulosic feedstocks, has attracted tremendous interest (owing to the large availability and low cost of this biomass) as a strategy to produce biofuels and commodity chemicals that is an alternative to oil refining. However, the innate recalcitrance of lignocellulose has slowed progress toward economically viable processes. Consolidated bioprocessing (CBP), i.e., single-step fermentation of lignocellulose may dramatically reduce the current costs of 2nd generation biorefining. Metabolic engineering has been used as a tool to develop improved microbial strains supporting CBP. Clostridium thermocellum is among the most efficient cellulose degraders isolated so far and one of the most promising host organisms for application of CBP. The development of efficient and reliable genetic tools has allowed significant progress in metabolic engineering of this strain aimed at expanding the panel of growth substrates and improving the production of a number of commodity chemicals of industrial interest such as ethanol, butanol, isobutanol, isobutyl acetate and lactic acid. The present review aims to summarize recent developments in metabolic engineering of this organism which currently represents a reference model for the development of biocatalysts for 2nd generation biorefining.
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